Hollow plastic containers are conventionally fabricated by blowing the containers to the internal confines of a mold cavity formed by a pair of opposed mold segments. The containers must be designed so that they can be removed from the mold after blowing. This requires that any undercuts must be shallow enough to permit the container to be stripped from the mold when the mold is opened. This limits the push-up height that can be achieved, and requires that the cross section of the container have a positive draft toward the mold parting line. A general object of the present invention is to provide a method and apparatus for molding hollow plastic containers having improved versatility in terms of the geometries, features and contours of the containers that can be molded.
A presently preferred but exemplary implementation of the invention deals with fabrication of self-draining containers, most preferably in a continuous extrusion wheel-type manufacturing process. Self-draining containers of this exemplary type are conventionally employed for packaging laundry products, and are illustrated for example in U.S. Pat. Nos. 4,989,757, 5,114,659, 5,207,356, 5,429,786 and 6,123,231. In general such containers include a hollow body, and an outlet portion with a pour spout, a collar surrounding the pour spout and having internal threads for securing a closure, a channel between the collar and the spout with an angulated bottom surface to capture any liquid that drips from the spout, and an opening at the low point of the angulated surface for draining the liquid back into the container. Current wheel-type manufacturing processes for containers of this type are not well suited for molding the drainback system as one piece integral with the container body and possessing high-definition internal threads. Continuous extrusion wheel-type processes for fabricating containers are illustrated, for example, in U.S. Pat. Nos. 4,523,904, 4,549,865, 4,648,831, 5,645,870 and 5,939,014. In processes of this type, an extruder provides a continuous hollow tube of plastic material. A plurality of molds are mounted around the periphery of a wheel, and the extruded tube is oriented tangentially of the wheel at a position aligned with the mold pairs as they pass in sequence. In general, portions of the tube are captured between opposed mold segments of each pair in sequence and blow molded to form containers. The central axis of each mold cavity in sequence is aligned with the extruded tube.
In a method of molding a hollow plastic container in accordance with preferred embodiments of the present invention, at least three mold segments are closed around a hollow tube of plastic material having a longitudinal axis by moving at least two of the mold segments toward the third mold segment in directions that are non-parallel to the axis of the tube. The mold segments when closed form a mold cavity that surrounds and captures a portion of the tube. A blow needle or pin on one of the mold segments pierces the tube when the mold segments are closed around the tube, and the tube is blown through the blow pin to the internal confines of the mold cavity. The mold cavity is then opened and the blown container is removed from the mold.
In the preferred but exemplary embodiment of the present invention, one of the mold segments comprises a mold core that is movably mounted on one of the other mold segments. The mold core is movable on the other mold segment between an extended position adjacent to the tube when the mold is closed, and a retracted position spaced from the tube. The blow pin may be mounted, either fixedly or movably, on the mold core or one of the other mold segments. In the exemplary preferred embodiment of the invention, the blow pin is movably mounted on the mold core for movement between an extended position that pierces the wall of the tube when the mold core is extended, and a retracted position spaced from the wall of the tube. Provision of a mold core movably mounted on another segment allows molding of plastic containers having contours, features and geometries that have not been blow-moldable to date, including containers having deep undercuts, containers having elaborate cross sections such as star-shaped cross sections, and containers with recesses along the mold parting line for storing devices such as trigger sprayers for the home/garden industry, for example.
A mold system for blow molding hollow plastic containers in accordance with an exemplary presently preferred embodiment of the invention includes an extruder for providing a hollow tube of plastic material having a longitudinal axis. The extruded tube may be of monolayer construction, or may be of multilayer construction including various layers of plastic resin material and/or adhesive material for obtaining desired properties in the container. A plurality of at least three mold segments include at least two mold segments that are movable against a third mold segment, in directions perpendicular to the tube axis, between a closed position in which the mold segments form a hollow mold cavity in which the tube is captured and an open position spaced from the tube axis. A blow pin is disposed on one of the mold segments to pierce the tube in the closed positions of the mold segments. One of the mold segments preferably comprises a mold core movably mounted on a second of the mold segments, and cylinders are mounted on the second mold segment for moving the mold core between an extended position and a retracted position with respect to the second mold segment. The blow pin preferably is movably mounted on the mold core.